Historically, the performance of an internal combustion engine has been limited by fixed valve lift profiles, i.e., fixed timing of the opening and closing of the valves relative to the angular position of the engine crankshaft and fixed lift of the valves. However, modern internal combustion engines may utilize one of several methods and/or devices to vary the valve lift profile to, at least in part, control the flow of gas and/or air into and/or out of the engine cylinders. Modern internal combustion engines may utilize devices, such as, for example, variable valve actuating mechanisms, two-step cam profile switching mechanisms (i.e., variable valve lift devices (VVL)), and deactivation valve lifters to vary the amount by which the valves of an engine are lifted (i.e., opened). Furthermore, engines may utilize devices, such as variable valve actuating mechanisms and cam phasers, to vary the timing of the opening and/or closing of the engine valves relative to the angular position of the engine crankshaft.
One such example of a variable valve lift device is a two-step cam profile switching mechanism. Two-step cam profile switching mechanisms utilize a two-step cam profile switching device, such as, for example, a two-step roller finger follower (RFF), to switch between two discrete valve lift profiles depending at least in part upon engine operating conditions and/or parameters. Two-step systems are relatively simple and are operable over a relatively wide range of engine operating speeds. Further such systems are relatively easy to package on new and even existing engines. By operating the two-step cam profile switching mechanism in conjunction with a cam phaser a wide range of variation in the valve lift characteristic is obtained. The valve lift profile is selected via the two-step cam profile-switching device, and the timing of the valve lift is adjusted and/or varied by the cam phaser.
Currently there are no reliable methods for determining whether one or more variable valve devices such as the two-step cam profile switching mechanisms used in an internal combustion engine are in an improper mode of operation. One existing method for diagnosing the operational state of a two-step cam profile switching mechanism involves the use of existing sensors or requires that additional sensors be integrated into the engine control system solely for diagnostic purposes. One drawback in using existing or integrated sensors to monitor the operational state of the two-step cam profile switching mechanism is that the engine control system that receives the diagnostic signal encounters a poor signal-to-noise. (S/N) ratio. The poor signal-to-noise ratio makes it difficult for the engine diagnostic system to extract a meaningful signal from a high level of background or ambient noise, which may create a situation where the diagnosis of the operational state of the two-step cam profile switching mechanism is unclear. For instance, if the difference in the signals representing a proper mode of operation and improper mode of operation is relatively small, a poor signal-to-noise (S/N) ratio could cause the measured signal to fall in between the signals representing the proper and improper modes of operation, thereby making it difficult to determine the operational state of the two-step cam profile switching mechanism. Since the signal received by the engine diagnostic system could be unclear as to which lift mode the two-step cam profile switching mechanism is operating under, there is no way to reliably determine if the two-step cam profile switching mechanism is operating properly and efficiently.
As the automotive industry migrates to multi-valve engines, ganged or grouped control of individual two-step cam profile switching mechanisms, and multiple lift profiles that are not dissimilar, the ability to diagnose a malfunctioning two-step cam profile switching mechanism will become more difficult. Misdiagnosed or undiagnosed two-step cam profile switching mechanisms could result in emissions non-compliance or the failure of the two-step cam profile switching mechanism or the engine.
What is needed in the art is a method for reliably and accurately determining the operational state of a variable valve lift device.
It is a principal object of the present invention to provide a method for reliably and accurately determining the operational state of a variable valve lift device.